1. Field of the Invention
The present invention relates to non-invasive ventilation and pressure support systems that use a patient interface device to deliver a flow of breathing gas to the airway of a patient, and, in particular, to a fluid coupling conduit, such as an elbow conduit, for such a patient interface device that includes a mechanism for reducing noise associated with the exhaust gas flow.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver positive airway pressure (PAP) therapy to treat certain medical disorders, the most notable of which is obstructive sleep apnea (OSA). Known PAP therapies include continuous positive airway pressure (CPAP), wherein a constant positive pressure is provided to the airway of the patient in order to splint open the patient's airway, and variable airway pressure, wherein the pressure provided to the airway of the patient is varied with the patient's respiratory cycle. Such therapies are typically provided to the patient at night while the patient is sleeping.
Non-invasive ventilation and pressure support therapies as just described involve the placement of a patient interface device including a mask component having a soft, flexible cushion on the face of a patient. The mask component may be, without limitation, a nasal mask that covers the patient's nose, a nasal cannula having nasal prongs that are received within the patient's nares, a nasal/oral mask that covers the nose and mouth, or a full face mask that covers the patient's face. Such patient interface devices may also employ other patient contacting components, such as forehead supports, cheek pads and chin pads. The patient interface device is connected to a gas delivery hose and interfaces the ventilator or pressure support device with the airway of the patient, so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient. It is known to maintain such devices on the face of a wearer by a headgear having one or more straps adapted to fit over/around the patient's head.
For patient interface devices used in, for example, the treatment of OSA, a key engineering challenge is to balance the exhaust gas flow and the exhaust gas noise. A certain amount of exhaust gas flow is required for all such patient interface devices to properly expel as much CO2 as possible. The amount of exhaust gas flow currently required to expel the proper amount of CO2 also makes the patient interface devices somewhat noisy. This noise could disturb a patient or bed partner, sometimes to the point where he or she will not be able to fall asleep or will be woken up inadvertently.
Most current patient interface devices utilize an elbow conduit for controlling the exhaust gas flow through small orifices. These orifices are molded in such a way to reduce noise as much as possible. Due to orifice complexity, most exhalation/exhaust ports are molded as separate pieces and assembled to form a complete elbow. Currently, no balance has been achieved in maintaining acceptable flow levels and low noise thresholds utilizing small orifices alone. Thus, an important opportunity exists for achieving acceptable flow levels and low noise thresholds.